Production of alpha-hydroxy isobutyric and methacrylic acids and their esters



Vmer(NO2) and the dimer (N204).

Uni

l2,811,546 ICC patented oct. 29,1957

PRDUCTION F a-HYDRXY ISOBUTYRIC AND METHACRYLIC ACDS AND THEIR ESTERSNat C. Robertson, Wellesley, and Thomas R. Steadman,

Waban, Mass., assignors to Escambia Chemical Corporation, Pace, Fia., acorporation of Delaware Continuation of application Serial No. 361,272,.lune 12, 1953. This application September 11, 1956, Serial No. 610,044

11 Claims. (Cl. Zoll-436) l1953 now abandoned and a continuation of ourcopending application ySerial No. 361,272 filed June l2, 1953 and nowabandoned.

A principal object of the present invention is to provide an economicalintegrated process for making methacrylic acid and esters thereof fromconstituents of natural gas such as isobutane.

v Another object of the invention is to provide an iml :proved processfor the production of the valuable intermediate compound alphahydroxyisobutyric acid.

Still another object of the invention is to provide an improved processfor oxidizing isobutylene glycol to alpha hydroxyisobutyric acid.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the process involving the severalsteps and the relation and the order of one or more of such steps withrespect to each of the others which are exemplified in the followingdetailed disclosure, and the scope of the application of which will beindicated in the claims. l,

For a .fuller understanding of Vthe nature and objects of the invention,reference vshould be had to the following detailed description taken inconnection with the accompanying drawing which is a flow sheetillustrating one f preferred embodiment of the present invention.

Methacrylic acid and its esters, such as the ethyl and methylmethacrylates, are very valuable chemicals which vhave found wideutility in the plastic industry. The production of these chemicals has,in the past, involved relatively complex procedures and has required theuse of relatively expensive starting materials. In the presentinfvention constituents of natural gas, such as isobutane, may

be utilized as the starting material. As explained in the copendingapplication of Robertson et al., Serial No. 316,158, filed October 22,1952, it is economically possible to oxidize isobutane to obtain highyields of isobutylene glycol.

The present invention is particularly directed to the conversion ofisobutylene glycol to methacrylic acid or esters thereof. A particularaspect of the present inven- -tion 'is directedkto the selectiveoxidation of isobutylene glycol so that only the primary hydroxyl groupthereof is converted to the Vcarboxyl group. ln one preferred,embodiment of the invention the isobutylene glycol is .oxidized bymeans of dinitrogen tetroxide (N204) to alpha hydroxyisobutyric acidwhiclris subsequently converted to methacrylic acid .or suitable estersthereof. Dinitrogen tetroxide is an equilibrium mixture of the mono- Theequilibrium concentration of the monomer is a function of temperature asdescribed in Ephraim Inorganic Chemistry, page i667, 3rd edition,Nordeman. When used in the specilicaf tion and the claims the expressiondinitrogen tetroxide is intended to include the equilibriumconcentration of the monomer at the temperature employed.

The reaction between the isobutylene glycol and dinitrogen tetroxidepreferably takes place with at least a stoichiometric amount of thedinitrogen tetroxide necessary to selectively oxidize the primaryhydroxyl group of the isobutylene glycol. This reaction is preferablycarried out at a relatively low temperature. The oxidation alsopreferably takes place in the presence of a substantial amount of acatalyst selected from the group consisting of the hydroxides,carbonates, nitrates, and nitrites of sodium, potassium, lithium, andbarium, and the oxides of aluminum and iron.

Referring now to the drawing, there is illustrated a flow sheet whichembodies one method of practicing the present invention. In the flowsheet there are shown a plurality of oxidation reactors indicated by thenumeral 8. For the sake of simplicity only two such reactors are shown,although there may be more than two. Each reactor 8 is arranged to befed with the preferred quantities of reactants. The dinitrogen tetroxideis supplied to the reactors i3 from a storage tank 2, and is mixed withthe preferred proportions of isobutylene glycol and a suitable basiccatalyst (e. g.,ppotassium carbonate) supplied from storage sources 4and 6, respectively. Upon completion of the controlled dinitrogentetroxide oxidation of isobutylene glycol to alpha hydroxyisobutyricacid, the reaction mixture is drained into chamber lili wherein a streamof dry air is blown over or through the reaction mixture so as to removeany volatile nitrogen compounds (e. g., NO and NO2) and tosimultaneously oxidize NO to NO2. The volatile nitrogen compoundsremoved in this manner escape at the top of chamber ltland are passedthrough condenser 14, The dinitrogen tetroxide thus recovered isrecycled back to the storagertanky 2. If desired, a suitable purifyingmeans may be employed prior to returning the recovered dinitrogentetroxide to the storage tank.

The reaction mixture, substantially freed of oxides of nitrogen, is runinto chamber l2 where it is treated with a saturated water solution ofurea, sulfamic acid or the like to destroy any residual nitrogencompounds. The resulting aqueous solution is then pumped to a continuousextractor 18, where it is extracted with a suitable solvent such asethylene dichloride. The ethylene dichloride solution of alphahydroxyisobutyric acid so obtained is fed to an esterication anddehydration reactor 2i). Sullicient quantities of sulfuric acid and analcohol (e. g., methanol) from supply sources 22 and 26, respectively,are added to the ethylene dichloride solution of alpha hydroxyisobutyricacid so as to simultaneously esterify and dehydrate the acid to methylmethacrylate. The esterilication and dehydration is carried out in thepresence of a small quantity of methylene blue (or any other suitablepolymerization inhibitor) supplied from source 24 so as to preventpolymerization. The resulting acidic solution of methyl methacrylate isthen neutralized at 28 with a calcium carbonate ysolution from supply30. The neutralized mixture is then passed through filter 32 to removeany insoluble materials such as calcium sulfate. The filtrate is runinto a continuous distillation still 34 wherein the various componentsof the filtrate are separated. The solvent, ethylene dichloride, andunreacted methanol are recovered. Thel methanol is preferably separatedfrom the ethylene dichloride before returning these products back totheir respective supplies.` The methyl methacrylate recovered from thedistillation still 34 may be led to suitable storage tanks or tosuitable purifying means.

Specific detailed methods of'practicing thejpresent invention are setforth in the following nonlirniting examf i ples which are directed morespecically to the step of oxidizing the isobutylene glycol to alphahydroxyisobutyric acid. y

Example I 10.2 grams of isobutylene glycol were charged to a reactionvessel and cooledin an ice bath at 0- C. f The cooled glycol was mixedwith 15.0 grams of dinitrogen tetroxide (NOM-N200 alsocooled to 04 C.andthe reaction mixture was maintained at substantially C. for 48 hours.At the end of this time, the major portion of the nitrogen oxidespresent were removed by passing a stream of dry air over the reactionmixtureV for a period of 30 minutes. The residual nitrogen oxidespresent were destroyed by adding a saturated solution of urea in waterat room temperature until no further evolution of gases occurred. Theresulting solution was made alkaline with sodium hydroxide and extractedcontinuously with diethyl ether for hours. The ether was then evaporatedor' on a steam bath and the residue was analyzed for unreacted glycol.The alkaline solution was made acidic with an inorganic acid (H2804,HC1, etc.) and then extracted with ether. The ether was evaporated olfon a steam bath and the residue was dissolved in benzene and freed ofwater by yazeotropic distillation. The dry benzene solution wasevaporated to a small volume, cooled, and a crop of crystals of alphahydroxyisobutyric acid amounting to 4.9 grams resulted.` The yield ofalpha hydroxyisobutyric acid was thus 41.8 percent of the theoreticalbased on the original quantity of isobutylene glycol charged. 5.6 wt.percent of other acids were recovered from the alpha hydroxyisobutyricacid mother liquors. 1.21 grams of isobutylene glycol were alsorecovered by evaporation of the ether solution obtained by extraction ofthe alkaline reaction mixture.

Although the` oxidation proceeds smoothly to produce reasonably goodyields of alpha hydroxyisobutyric acid in the absence of catalysts, evenhigher yields may be obtained by the use of a suitable basic catalyst asshown in the following example.

Example Il 9.98 grams of isobutylene glycol, 5.0 grams of potassiumcarbonate (KzCOa) and 50 rnl. of dinitrogen tetroxide (NO2 N2O4) werecharged to a reaction vessel. The reaction mixture was maintained atsubstantially room temperature C.) for 24 hours. At the end of wassaturated with potassium carbonate and then extracted y with butanol.The butanol extract was analyzed for any unreacted glycol. The aqueoussolution was made acidic and extracted with ether. The ether wasevaporated off on a steam bath, and the residue was dissolved in benzeneand freed of water by azeotropic distillation. The dry benzene solutionwas evaporated to a small volume, cooled, and a crop of alphahydroxyisobutyric acid crystals amounting to 7.14 grams resulted. Thisoxidation of isobutylene glycol resulted in a yield of alphahydroxyisobutyric acid of 61.8 percent of theoretical based on theisobutylene glycol charged. A small percent of isobutylene glycol andunidentified acidic material was also recovered.

Example III Isobutylene glycol was oxidized under conditions similar tothose described in Example II except for the fact that 4.4 grams ofsodium hydroxide were used in place of the potassium carbonate to give ayield of 51.6 percent of alpha hydroxyisobutyric acid.

i l Example IV Isobutylene glycol was oxidized under conditions similarto those described in Example II except for the fact that 21.7 grams ofbarium carbonate were used in place of the potassium carbonate to give ayield of 54.0 percent of alpha hydroxyisobutyric acid.

Example V Isobutylene glycol was oxidized under conditions similar tothose described in Example II except for the fact that 7.5 grams ofalumina (A1203) were used in place of the potassium carbonate to give ayield of 42.2 percent of alpha hydroxyisobutyric acid.

Example VI Isobutylene glycol was oxidized under conditions similar tothose described in Example II except for the fact that 11.7 grams ofiron oxide (FezOs) were used in place of the potassium carbonate to givea yield of 40.0 percent of alpha hydroxyisobutyric acid.

Example VII Isobutylene glycol was oxidized under conditions similar tothose described in Example II except for the fact that 6.2 grams ofpotassium hydroxide were used in place of the potassium carbonate togive a yield of 47.8 percent of alpha hydroxyisobutyric acid.

Example VIII Isobutylene glycol was oxidized under conditions similar tothose described in Example II except for the fact that 6.72 grams oflithium carbonate were used in place of potassium carbonate to give ayield of 48.0 percent of alpha hydroxyisobutyric acid.

Example IX rated solution of sulfamic acid in water at room temperatureuntil no further evolution of gases occurred. The resulting solution wasmade basic with sodium hydroxide and then saturated with potassiumcarbonate followed by a butanol extraction. The butanol extract wasanalyzed for any unreacted glycol. The aqueous solution was made acidicwith sulfuric acid to a pH of 1 and extracted with ether for 24 hours.The ether was evaporated off on a steam bath and the residue wasdissolved in benzene and freed of water by azeotropic distillation. Thedry benzene solution was evaporated to a small volume, cooled, and acrop of alpha hydroxyisobutyric acid crystals amounting to 5.42 gramsresulted. This oxidation of isobutylene glycol resulted in a yield ofalpha hydroxyisobutyric acid of 48.3 percent of theoretical based on theisobutylene glycol charged. 14.1 percent of unreacted isobutylene glycolwas also recovered.

Example X Example XI Isobutylene glycol was oxidized under conditionssimilar -to those described in Example 1X except for the fact that 9.35grams of sodium nitrate (NaNOa) were used in place of potassium nitrateto give a yield of 66.0 percent of alpha y hydroxyisobutyric acid. 14.5percent of unreacted isobutylene glycol was also recovered.

This oxidation as'described in the preceding examples proceedsessentially as follows:

The oxidation of isobutylene glycol will take place when at least thestoichiometric amount of dinitrogen tetroxide required for the reactionis present. However, better results have been obtained when there is anexcess of oxidizing agent present. The excess dinitrogen tetroxidepresent may be varied over a wide range, but it has been foundpreferable to use an amount of the dinitrogen tetroxide which is atleast 50 percent in excess over the stoichiometric amount needed toselectively oxidize the primary alcohol group.

The reaction may be carried out at a temperature in the range of from 0C. to 35 C. and in the presence 0r absence of any suitable solvents.However, the use of a solvent is less desirable since reactionsemploying solvents such as acetic acid, ether, and chloroform have in noin stance produced yields of alpha hydroxyisobutyric acid as high asthose obtained in the absence of solvents.

The time `of reaction may be varied so that, for example, very muchshorter periods are satisfactory. Yields of product amounting to 35%were obtained with sodium carbonate present, with a reaction time of onehour. Under such circumstances, however, substantial quantities of theisobutylene glycol are recovered unchanged.

As pointed out above, the present process Amay be satisfactorilypracticed without the aid of a catalyst. However, the presence ofcatalysts have given considerably higher yields. The preferred catalystsare carbonates, hydroxides, nitrates, and nitrites of sodium, potassium,lithium, and barium. Such compounds as NaOH, KOH, NazCOs, NaHCOs, K2CO3,BaCO3, LizCOa, KNOs, KNOz, NaNOs, etc. are all satisfactory catalysts.It has also been found that oxides of iron and aluminum may also beemployed as catalysts.

When catalysts such as the carbonates and hydroxides (or oxides) areemployed, it is believed that an appreciable amount of nitrates and/ ornitrites are formed from the hydroxides (or oxides) and carbonatesduring the oxidation reaction. Thus, in all dinitrogen tetroxideoxidations employing a catalyst of the above mentioned preferred groups,there may also be present the corresponding nitrates and/ or nitrites.

As pointed out above, upon completion of the oxidation most of thenitrogen oxides present are removed from the reaction mixture by passinga stream of dry air over or through the mixture. This also converts anydissolved NO to NO2. The small amounts of residual dinitrogen tetroxidestill in the reaction mixture can then be destroyed by the addition of asaturated water solution of urea, hydrazine, or sulfamic acid, or othersimilar compounds.

'Ihe extraction of the desired acid from the reaction mixture may bedone by any of the well-known chemical procedures. Other methods ofseparation than those dcscribed may be employed such as, for example,the removal of the acid by formation of the insoluble zinc salt.

In connection with the specific ow sheet illustrated in the drawing, itshould be pointed out that numerous modications may be made in thevarious techniques employed without departing from the scope of theinvention. For example, if methacrylic acid is the desired end productrather than the methacrylate, the esteritication step is eliminated andthe alpha hydroxyisobutyric acid is simply dehydrated to methacrylicacid by use of a suitable strong mineral acid, such as sulfuric orphosphoric acids.

Equally, many esters of methacrylic acid other tha-n the methyl estermay be made by utilizing a dilerent alcohol. Examples of such suitablealcohols are the aliphatic straight chain alcohols ethyl, propyl, butyl,etc. In a similar manner, the specific reagents employed in the variousneutralization and reaction stepsV may be replaced by numerousequivalent chemicals. For example, the ethylene dichloride solvent canbe replaced by numerous other solvents such as methylene dichloride,carbon tetrachloride and similar low-boiling halogenated hydrocarbons.Numerous other acids and bases maybe used in place of the lspeciiiclreagents (H2804 and CaCOs) employed in the illustrated llow sheet. Inlike manner, many other polymerization inhibitors such as para tertiarybutyl catechol or hydroquinone may be substituted for the methyleneblue.

Since certain changes may be made in the above process without departingfrom the scope of the invention herein involved, it is intended that allmatter contained in the above description, or shown in the accompanyingdrawing, shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

l. A process for the production of methacrylates which comprises thesteps of oxidizing isobutylene glycol with dinitrogen tetroxide, saiddinitrogen tetroxide being used in at least 5() percent excess of thestoichiometric amount required to selectively oxidize the primaryalcohol group to form alpha hydroxyisobutyric acid, esterifying saidalpha hydroxyisobutyric acid with a primary aliphatic alcohol to formthe corresponding ester, and dehydrating the ester to form themethacrylate.

2. A process for the production of methacrylates which comprises thesteps of oxidizing isobutylene glycol with dinitrogen tetroxide, saiddinitrogen tetroxide being used in at least 50 percent excess of thestoichiometric amount required to selectively oxidize the primaryalcohol group to form alpha hydroxyisobutyric acid, esterifyi-ng saidalpha hydroxyisobutyric acid with an alcohol to form the correspondingester, and dehydrating the ester to form the methacrylate.

3. A process for the production of methacrylic acid which comprises thesteps of oxidizing isobutylene glycol with dinitrogen tetroxide, saiddinitrogen tetroxide being used in at least 50 percent excess of thestoichiometric amount required to selectively oxidize the primaryalcohol group to form alpha hydroxyisobutyric acid, and dehydrating saidacid to form methacrylic acid.

4. A process for the production of alpha hydroxyisobutyric acid whichcomprises oxidizing isobutylene glycol with dinitrogen tetroxide, saiddinitrogen tetroxide being used in at least 50 percent excess of thestoichiometric amount required to selectively oxidize the primaryalcohol group.

5. A process for the production of esters of alpha hydroxyisobutyricacid which comprises oxidizing isobutylene glycol with dinitrogentetroxide, said dinitrogen tetroxide being used in at least 50 percentexcess of the stoichiometric `amount required to selectively oxidize theprimary alcohol group to form alpha hydroxyisobutyric acid, andesterifying said alpha hydroxyisobutyric acid with an alcohol to formthe corresponding ester.

6. A process for the production of alpha hydroxyisobutyric acid whichcomprises oxidizing isobutylene glycol with dinitrogen tetroxide in thepresence of a catalyst from the group consisting of the hydroxides,carbonates, nitrates, and nitrites of sodium, potassium, lithium, andbarium, and the oxides of iron and aluminum, said dinitroge-n tetroxidebeing used in at least 50 percent excess of the stoichiometric amountrequired to selectively oxidize the primary alcohol group, and isolatingalpha hydroxyisobutyric acid from said reaction mixture.

7. A process according to claim 6 wherein said catalyst is alumina.

8. A process according to claim 6 wherein said catalyst is ferrie oxide.

9. The process of claim 6 wherein said catalyst comprises potassiumcarbonate.

10. The process of claim 6 wherein said catalyst cornprises potassiumnitrite.

7 8 11.` The process of claim 6 wherein said catalyst com- 2,356,247Kirk et al. Aug. 22, 1944 prises sodium nitrate. 2,360,880 Kropa Oct.24, 1944 References Cited in the file of this patent OTHER REFERENCESUNITED STATES PATENTS 5 Klemenc: Chem. Abst. 42 (1948) 62211'. 2,267,377Olin Dec' 23, 1941 Degel'ing et 3.1.1 J. Am. Chem. SOC. 73 (1951) 848-9.2,298,387

Kenyon Oct 13' 1942 Groggins: Unit Processes, 4th ed. (1952) 425-6.

1. A PROCESS FOR THE PRODUCTION OF METHACRYLATES WHICH COMPRISES THESTEPS OF OXIDIZING ISOBUTYLENE GLYCOL WITH DINITROGEN TETROXIDE, SAIDDINITROGEN TETROXIDE BEING USED IN AT LEAST 50 PERCENT EXCESS OF THESTOICHIOMETRIC AMOUNT REQUIRED TO SELECTIVELY OXIDIZE THE PRIMARYALCOHOL GROUP TO FORM ALPHA HYDROXYISOBUTYRIC ACID, ESTERIFYING SAIDALPHA HYDROXYISOBUTYRIC ACID WITH A PRIMARY ALIPHATIC ALCOHOL TO FORMTHE CORRESPONDING ESTER, AND DEHYDRATING THE ESTER TO FROM THEMETHACRYLATE.